1. Field of the Invention
This invention relates to a process for producing a solid catalyst for polymerization of olefins. More specifically, it relates to a process for producing a solid catalyst for polymerization of olefins by using a solution of an aluminoxane, a particulate carrier having a transition metal compound supported thereon, and a solvent in which the aluminoxane is insoluble or sparingly soluble.
2. Description of the Prior Art
Conventional processes for producing alpha-olefin polymers, especially an ethylene homopolymer or an ethylene/alpha-olefin copolymer involve polymerizing ethylene or copolymerizing ethylene and an alpha-olefin in the presence of a titanium catalyst composed of a titanium compound and an organoaluminum compound or a vanadium catalyst composed of a vanadium compound and an organoaluminum compound. Generally, ethylene/alpha-olefin copolymers obtained with the titanium catalysts have a broad molecular weight distribution and a broad composition distribution and have inferior transparency, freedom from surface tackiness and dynamical properties. Ethylene/alpha-olefin copolymers obtained with the vanadium catalysts have a narrower molecular weight distribution and a narrower composition distribution than those obtained with the titanium catalysts, and show a considerable improvement in transparency, freedom from surface tackiness and dynamical properties. However, these catalysts have low polymerization activity, and it is necessary to remove the catalysts from the resulting polymers. It is desired therefore to elevate the polymerization activity of these catalysts.
Recently, catalysts composed of zirconium compound and aluminoxanes were proposed as a new type of Ziegler catalysts for polymerization of alpha-olefins.
Japanese Laid-Open Patent Publication No. 19,309/1983 describes a process for polymerizing ethylene and at least one alpha-olefin having 3 to 12 carbon atoms at a temperature of -50.degree. C. to 200.degree. C. in the presence of a catalyst formed from a transition metal-containing compound represented by the following formula EQU (cyclopentadienyl).sub.2 MeRHal
wherein R represents cyclopentadienyl, C.sub.1 -C.sub.6 alkyl, or halogen, Me represents a transition metal, and Hal represents halogen, and a linear aluminoxane represented by the following formula EQU Al.sub.2 OR.sup.4 (Al(R)-O).sub.n
wherein R is methyl or ethyl and n is a number of 4 to 20, or a cyclic aluminoxane represented by the following formula ##STR1## This patent document describes that to adjust the density of the resulting polyethylene, the polymerization of ethylene should be carried out in the presence of up to by weight of an alpha-olefin having a slightly long chain or its mixture.
Japanese Laid-Open Patent Publication No. 95,292/1984 describes a process for producing a linear aluminoxane represented by the following formula ##STR2## wherein n is 2 to 40, and R is C.sub.1 -C.sub.4 hydrocarbon group, and a cyclic aluminoxane represented by the following formula ##STR3## wherein n and R are as defined above. This patent document discloses that an ethylene is polymerized in the presence of a mixture of methylaluminoxane with a bis(cyclopentadienyl) compound of zirconium, polyethylene can be obtained in an amount of at least 25 million grams per gram of the transition metal per hour.
Japanese Laid-Open Patent Publication No. 35,005/1985 discloses a process for producing a catalyst for polymerization of olefins, which comprises reacting an aluminoxane compound represented by the following formula ##STR4## wherein R.sup.1 is C.sub.1 -C.sub.10 alkyl, and R.sup.o is R.sub.1 or is bonded to R.sup.1 to represent --O--, with a magnesium compound, then chlorinating the reaction product, and treating the chlorinated product with a compound of V, Zr or Cr. This patent document describes that the resulting catalyst is especially suitable for copolymerization of a mixture of ethylene with a C.sub.3 -C.sub.12 alpha-olefin.
Japanese Laid-Open Patent Publication No. 35,006/1985 discloses a combination of (a) two or more dissimilar mono-, di- and tri-cyclopentadienyls or their derivatives of transition metals and (b) an aluminoxane as a catalyst for preparation of reactor blended polymers. Example 1 of this Japanese Laid-open Patent Publication shows that ethylene and propylene are polymerized in the presence of a catalyst composed of bis(pentamethylcyclopentadienyl)dimethyl zirconium and an aluminoxane to provide polyethylene having a number average molecular weight of 15,300, a weight average molecular weight of 36,400 and a propylene content of 3.4%. In Example 2 of this patent document, ethylene and propylene are polymerized in the presence of a catalyst composed of bis(methylcyclopentadienyl)zirconium dichloride and an aluminoxane to afford a blend of polyethylene and an ethylene/propylene copolymer consisting of a toluene-soluble portion having a number average molecular weight of 2,200 and a weight average molecular weight of 11,900 and containing 30 mole % of a propylene component and a toluene-insoluble portion having a number average molecular weight of 3,000 and a weight average molecular weight of 7,400 and containing 4.8 mole % of a propylene component, said blend having a number average molecular weight of 2,000 and a weight average molecular weight of 8,300 and containing 7.1 mole % of a propylene component. Example 3 of this document describes a blend of LLDPE and an ethylene-propylene copolymer consisting of a soluble portion having a molecular weight distribution (Mw/Mn) of 4.57 and containing 20.6 mole % of a propylene component and an insoluble portion having a molecular weight distribution of 3.04 and containing 2.9 mole % of a propylene component.
Japanese Laid-Open Patent Publication No. 35,007/1985 describes a process wherein ethylene alone is polymerized, or ethylene and an alpha-olefin having 3 or more carbon atoms are copolymerized, in the presence of a catalyst composed of a metallocene and a cyclic aluminoxane represented by the formula ##STR5## wherein R represents an alkyl group having to 5 carbon atoms and n represents an integer of 1 to about 20, or a linear aluminoxane represented by the formula ##STR6## wherein R and n are as defined above. The patent document describes that the polymer yielded by the above process has a weight average molecular weight of about 500 to about 1,400,000 and a molecular weight distribution of 1.5 to 4.0.
Japanese Laid-Open Patent Publication No. 35,008/85 states that polyethylene or an ethylene/C.sub.3 -C.sub.10 alpha-olefin having a wide molecular weight distribution is produced by using a catalyst system composed of at least two metallocenes and aluminoxane. It discloses that the copolymer has a molecular weight distribution (Mw/Mn) of 2-50.
The catalysts formed from the transition metal compounds and aluminoxanes which are proposed in these prior art references have much higher polymerization activity than hitherto known catalyst systems composed of transition metal compounds and organoaluminum compounds. However, most of the catalyst systems proposed there are soluble in the reaction system and mainly used in solution polymerization. Accordingly, the viscosity of the polymerization system becomes very high, and the bulk density of the polymer obtained by after-treatment of the solution is low. It is difficult therefore to obtain a polymer having excellent powder properties.
On the other hand, attempts have been made to polymerize olefins by suspension polymerization or vapor-phase polymerization using catalysts wherein one or both of the aforesaid transition metal compounds and aluminoxanes are supported on carriers of porous inorganic oxides such as silica, silica/alumina and alumina.
For example, the above-cited Japanese Laid-Open Patent Publications Nos. 35,006/1985, 35,007/1985 and 35,008/1985 describe catalysts comprising transition metal compounds and aluminoxanes supported on silica, silica/alumina or alumina.
Japanese Laid-Open Patent Publications Nos. 106,808/1985 and 106,809/1985 propose a process for producing a composition composed of a polyethylene-type polymer and a filler formed by polymerizing ethylene or copolymerizing ethylene with an alpha-olefin in the presence of a substance obtained by previously contacting a highly active catalyst component containing titanium and/or zirconium and soluble in a hydrocarbon solvent with a filler, an organoaluminum compound, and a filler having affinity for polyolefins.
Japanese Laid-Open Patent Publication No. 31,404/1986 proposes a process for polymerizing ethylene or copolymerizing ethylene with an alpha-olefin in the presence of a catalyst mixture composed of a product obtained by reacting a trialkylaluminum with water in the presence of silicon dioxide and aluminum oxide, and a transition metal compound.
Japanese Laid-Open Patent Publication No. 276,805/1986 proposes a process for polymerizing an olefin in the presence of a catalyst composed of a zirconium compound and a reaction mixture obtained by reacting a reaction mixture of an aluminoxane and a trialkylaluminum with n inorganic oxide having a surface hydroxyl group such as silica.
Each of the carrier-supported solid catalysts proposed in the above prior art references is prepared by forming a suspension composed of the carrier and a solution of the aluminoxane and transition metal compound, evaporating the solvent from the suspension, and drying the residue. When olefins are polymerized or copolymerized in a suspension polymerization system or a vapor-phase polymerization system using these solid catalyst components, the polymerization activity of the solid catalyst components is much lower than in the case of performing the polymerization in the solution-polymerization system described above, and the inherent characteristics of the transition metal compound catalyst component and the aluminoxane catalyst component are not fully exhibited. Furthermore, the resulting polymers do not prove to be entirely satisfactory with regard to powder properties such as bulk density.